Adsorbent and method of collecting precious metal using the same

ABSTRACT

An adsorbent contains a carbohydrate having an ether linkage. Alternatively, an adsorbent contains a carbohydrate having a cross-linkage formation produced by a dehydration reaction using a strong acid. In collection of a precious metal using the adsorbent, the adsorbent selectively adsorbs a precious metal dissolved in a solution.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2011-39071filed on Feb. 24, 2011, the disclosure of which is incorporated hereinby reference.

TECHNICAL FIELD

The present disclosure relates to an adsorbent and a method ofcollecting a precious metal using the adsorbent.

BACKGROUND

Gold has been widely used as a plating material, electric and electronicmaterials, a medical material and the like, besides jewelry. As gold isexpensive, it has been desired to collect gold from various kinds ofwastage or waste fluid. However, the quantity of gold contained in thewastage is small, and it is difficult to selectively separate andcollect gold from other metals which exist in large amounts.

In a conventional method of collecting gold from various kinds-of solidwastage, the solid is dissolved in aqua regia, and gold is collectedfrom the solution by a metal substitution technique or the like.However, since the regulation on nitrogen in drainage has been recentlytightened, the collection using the aqua regia is getting difficult toimplement.

The following methods have been also proposed as methods of separatingand collecting precious metals:

(a) Solvent Extraction Method and Ion Exchange Method

A solvent extraction method and an ion exchange method have beenrecently adopted as methods for collecting precious metals from an anodeslime which is generated in an electrolytic smelting of copper, nickeland the like. In such a collecting process, after metals are completelydissolved in hydrochloric acid containing chlorine gas, the metals areindividually collected by the solvent extraction method or the ionicexchange method.

With regard to the collection of gold, a solvent extraction method usingdibutyl carbitol is adopted in many countries including Japan. Such asolvent extraction method is, for example, described in detail innon-patent document 1 listed below.

(b) Method Using Chemically-Modified Cellulose

Chemical modification of cellulose has been widely researched, and manyadsorbents have been put into practice for analytical chemistry andmedical use. For example, non-patent document 2 listed below describescellulose in detail.

For example, the cellulose in which various functional groups, such as adiethylaminoethyl (DEAE) group, is introduced by chemical modificationis used for separation and refinement of biogenic substances, such as anenzyme, a plasma component, and other functionality protein materials.

Moreover, there are some researches regarding collection of preciousmetals contained in various waste fluids and wastage using adsorbentsprepared by chemical modification of a cellulose-base material such aspaper. For example, non-patent document 3 listed below reports anadsorbent in which a primary amino group is fixed by the chemicalmodification of wastepaper.

<Non-Patent Document 1>

B. F. Rimmer, “Refining of gold from precious metal concentrates byliquid-liquid extraction”, Chemistry & Industry, Jan. 19, 1974, No. 2,pp. 63-66

<Non-Patent Document 2>

“Dictionary of cellulose”, pp. 131-165, “4.2 Chemical reaction ofcellulose and derivative”, and pp. 539-545, “7.5.4 Ion exchangematerial”, Cellulose Society of Japan

<Non-Patent Document 3>

KAWAKITA Hidetaka, INOUE Katsutoshi, OHTO Keisuke, ITAYAMA Kyoko,PARAJULI Durga, “Preparation of Amine-Type Adsorbent Using Wastepaperand Adsorption of Metal Ions”, Waste Management Research 17(3), May 31,2006, pp. 243-249

SUMMARY

It is an object of the present disclosure to provide an adsorbent, whichcan efficiently separate and collect a precious metal contained in asolution. It is another object of the present disclosure to provide amethod of collecting a precious metal from a solution.

An adsorbent according to an aspect contains a carbohydrate having anether linkage.

In collection of a precious metal using the adsorbent, the adsorbentselectively adsorbs a precious metal contained in a solution. Therefore,a precious metal in the solution can be selectively and efficientlyseparated and collected from the solution.

For example, a precious metal, such as gold, can be efficientlycollected from a solution, such as aqua regia or hydrochloric acidsolution in which wastage containing precious metals, such as gold,platinum and palladium, and base metals, such as iron, is dissolved.

An adsorbent according to another aspect contains a carbohydrate havinga cross-linkage formation produced by a dehydration reaction.

In collection of a precious metal using the adsorbent, the adsorbentselectively adsorbs a precious metal contained in a solution. Therefore,a precious metal in the solution can be selectively and efficientlyseparated and collected from the solution.

For example, a precious metal, such as gold, can be efficientlycollected from a solution, such as aqua regia or hydrochloric acidsolution in which wastage containing precious metals, such as gold,platinum and palladium, and base metals, such as iron, is dissolved.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentdisclosure will become more apparent from the following detaileddescription made with reference to the accompanying drawings. In thedrawings:

FIG. 1 is a diagram illustrating infrared absorption spectrums of acellulose processed with concentrated sulfuric acid, a celluloseprocessed with concentrated sulfuric acid and to which gold(III) ionsare adsorbed, and a raw material, according to an embodiment;

FIG. 2 is a graph illustrating a relationship between an adsorptionpercentage of gold ions and a concentration of hydrochloric acid when anadsorbent A of 102330 cellulose processed with a concentrated sulfuricacid is used, according to the embodiment;

FIG. 3 is a graph illustrating a relationship between an adsorptionpercentage of gold ions and a concentration of hydrochloric acid when anadsorbent B of cotton processed with concentrated sulfuric acid is used,according to the embodiment;

FIG. 4 is a graph illustrating a relationship between an adsorptionpercentage of respective metals and a concentration of hydrochloric acidin a solvent extraction using undiluted dibutyl carbitol, as acomparative example;

FIG. 5 is a graph illustrating a relationship between an adsorptionpercentage of respective metal ions and a concentration of hydrochloricacid, when a commercially available weakly basic ion exchange resinDIAION WA30 with a functional group of dimethylamine is used, as acomparative example;

FIG. 6 is a graph illustrating an adsorption isotherm of gold(III) at 30degrees Celsius, when the adsorbent A of cellulose processed with theconcentrated sulfuric acid is used, according to the embodiment;

FIG. 7 is a graph illustrating an adsorption isotherm of gold(III) at 30degrees Celsius when an adsorbent B of cotton processed with theconcentrated sulfuric acid is used, according to the embodiment;

FIG. 8 is a graph illustrating a solid-liquid ratio of the adsorbent Aand a residual concentration of gold according to the embodiment;

FIG. 9 is a graph illustrating a solid-liquid ratio of the adsorbent Band raw cotton and a residual concentration of gold according to theembodiment;

FIG. 10A is an optical micrograph of the adsorbent A after adsorption ofgold according to the embodiment;

FIG. 10B is an illustrative view of the optical micrograph shown in FIG.10A;

FIG. 11A is an optical micrograph of the adsorbent B after adsorption ofgold according to the embodiment; and

FIG. 11B is an illustrative view of the optical micrograph shown in FIG.11B.

DETAILED DESCRIPTION

In a solvent extraction using dibutyl carbitol (e.g., theabove-described method (a)), precious metals other than gold and basemetals are extracted, in addition to gold, depending on conditions.Therefore, multistage extraction and back extraction operations arerequired, resulting in an increase in the cost of separation andrefining. In addition, the dibutyl carbitol is considerably soluble inwater, resulting in an increase in the cost of waste water treatment.

With regard to the above-described method (b), the chemically-modifiedcellulose used in the technology of the non-patent document 2 isgenerally expensive. Further, in preparation of the chemically-modifiedcellulose used in the technology of the non-patent document 2, manypoisonous organic chemicals, such as epichlorohydrin and glutaraldehyde,are used, resulting in an increase in cost of safe treatment of theorganic chemicals which remains after the preparation.

Moreover, according to the technology of the non-patent document 3, inthe above-described method (b), although gold, platinum, and palladiumare adsorbed and collected from hydrochloric acid, an amount of copperas the base metal is also adsorbed.

In view of the foregoing matters, the following adsorbents are achievedas adsorbents which can efficiently separate and collect a preciousmetal, such as gold, from a solution, such as aqua regia or hydrochloricacid in which wastage containing gold is dissolved.

In an embodiment, an adsorbent contains a carbohydrate having an etherlinkage. In collection of a precious metal using the adsorbent, theadsorbent selectively adsorbs a precious metal contained in a solution.Therefore, a precious metal dissolved in the solution can be selectivelyand efficiently separated and collected from the solution.

For example, a precious metal, such as gold, can be efficientlycollected from a solution, such as aqua regia or hydrochloric acidsolution, in which wastage containing precious metals, such as gold,platinum and palladium, and base metals, such as iron, is dissolved.Further, the adsorbent can be produced without using expensive organicchemicals.

The above-described ether linkage can be formed by processing acarbohydrate, such as pure cellulose gel, with a strong acid, such asconcentrated sulfuric acid or concentrated hydrochloric acid, at a hightemperature, such as a temperature not less than 70 degrees Celsius (°C.), for example, 100° C.., to thereby form a cross-linkage by adehydration reaction.

In an embodiment, an adsorbent contains a carbohydrate having across-linkage formation produced by a dehydration condensation reaction.

In collection of a precious metal using the adsorbent, the adsorbentselectively adsorbs a precious metal contained in a solution. Therefore,a precious metal in the solution can be selectively and efficientlyseparated and collected from the solution.

For example, a precious metal, such as gold, can be efficientlycollected from a solution, such as aqua regia or hydrochloric acidsolution, in which wastage containing precious metals, such as gold,platinum and palladium, and base metals, such as iron, is dissolved.Further, the adsorbent can be produced without using expensive organicchemicals.

The carbohydrate of the above-described adsorbents is cellulose, forexample. The cellulose includes at least one of cotton, hemp and paper,for example.

A precious metal dissolved in a solution can be collected by adsorbingthe precious metal to the above-described adsorbents.

To remove the precious metal from the adsorbent, for example, theadsorbent to which the precious metal has been adsorbed is burned, and adesired precious metal is removed from the ashes.

In this case, the burning of the adsorbent advances readily, as comparedwith a plastic resin such as a chelating resin and an ion exchangeresin. Therefore, the precious metal is easily collected.

Hereinafter, the embodiments will be described more in detail referringto various examples.

<Preparation of Adsorbent>

The adsorbent is easily prepared by heating and mixing a cellulose-basematerial, such as pure cellulose gel, with concentrated sulfuric acidfor six hours or more at a temperature equal to or greater than 70degrees Celsius (° C.).

In place of the above-described cellulose gel, another cellulose-basematerial may be processed in the similar manner. Alternatively, inaddition to the cellulose gel, another cellulose-base material may beprocessed together in the similar manner.

As examples of the cellulose-base material other than the pure cellulosegel, cotton such as cotton products or old cotton clothes, hemp such ashemp fiber waste, paper such as wastepaper, are adopted.

For example, an adsorbent A is produced by processing a cellulose gel(e.g., 102330 Cellulose microcrystalline (Merck) distributed forthin-layer chromatography) with concentrated sulfuric acid in theabove-described manner.

FIG. 1 illustrates an infrared absorption spectrum A1 of the adsorbentA. Also, in FIG. 1, A2 represents an infrared absorption spectrum of theadsorbent A to which gold (III) ions are adsorbed, and A3 represents aninfrared absorption spectrum of a raw material, that is, cellulose gelof 102330 cellulose microcrystalline, which is not processed withconcentrated sulfuric acid. In FIG. 1, the horizontal axis represents awave number and the vertical axis represents an absorbance.

With regard to the raw material, broad absorption around 3450 cm⁻¹ iscaused by stretching vibration of O—H, and sharp absorption at 3050 cm⁻¹is caused by stretching vibration of C—H. Also, sharp absorption at 1720cm⁻¹ is caused by stretching vibration of C═0, and broad absorptioncentering on 1100 cm⁻¹ is caused by stretching vibration of C—O as wellas deformation vibration of alcoholic O—H.

With regard to the cellulose processed with the concentrated sulfuricacid, the intensity of absorption caused by the stretching vibrations ofO—H and C—H is degraded, and the cause thereof is considered because ofa dehydration condensation cross-linkage reaction by the concentratedsulfuric acid. Also, absorption at 1200 cm⁻¹ is caused by stretchingvibration of C—O—C which is produced by the dehydration condensationcross-linkage reaction. As such, it is considered that the hydroxylgroup is changed to C—O—C (ether linkage) as a result of the dehydrationcondensation cross-linkage reaction.

In the cellulose processed with the concentrated sulfuric acid, further,sharp absorption is found at 1780 cm⁻¹ and at 1690 cm⁻¹. The sharpabsorption at 1780 cm⁻¹ is caused by stretching vibration of C═O whichis produced by partial oxidation of the hydroxyl group of a pyranosering. The sharp absorption at 1690 cm⁻¹ is caused by stretchingvibration of C═O of a carboxyl group.

As described above, it is considered that the processing of thecellulose with the concentrated sulfuric acid causes the partialoxidation of the hydroxyl group.

With regard to the cellulose to which gold(III) ions are adsorbed,absorption caused by an acid group is broad, and is shifted to a lowwave number range around 3410 cm⁻¹. Thus, it is considered that thehydroxyl group is also participated in the coordination of the gold(III)ions. The intensity of absorption caused by C═O at 1690 cm⁻¹ isincreased after the adsorption of the gold(III) ions, and the causethereof is considered as —COOH group is generated due to the adsorptionof the gold(III) ions.

<Adsorption and Collection of Precious Metal>

Hereinafter, examples are described with regard to an evaluation ofadsorption of various kinds of metal ion to the above-describedadsorbent A in hydrochloric acid by a batch method.

In this case, as a precious metal solution, a solution prepared bydissolving chloroauric(III) acid, chloroplatinic(IV) acid, andpalladium(II) chloride as special grade chemicals in hydrochloric acidis used. Also, as a base metal solution, a solution prepared bydissolving hydrochlorides of copper(II) and zinc(II) in hydrochloricacid is used.

<Influence of Hydrochloric Acid Concentration on Adsorption of VariousKinds of Metal Ion>

10 mg in dry weight of the adsorbent A and 10 mL of hydrochloric acid ofvarious concentrations, each containing respective metal ions of theconcentration of 0.1 mmol/L are put in flasks with plugs, and shaken for24 hours in an air thermostatic reservoir kept at 30° C. to carry outadsorption. An adsorption percentage of each metal ion adsorbed to theadsorbent A is calculated by measuring the concentration of the metalion in the aqueous solution before and after the adsorption using an ICPemission spectrometer, (e.g., Spectrometer ICPS-8100 of SHIMADZUCorporation). The adsorption percentage is given based on the followingequation:

Adsorption percentage=(metal concentration in the aqueous solutionbefore the adsorption−metal concentration in the aqueous solution afterthe adsorption)/(metal concentration in the aqueous solution before theadsorption)×100

FIG. 2 is a graph illustrating a relationship between the concentrationof hydrochloric acid (horizontal axis) and the adsorption percentage(vertical axis) of metal ions, when the adsorbent A of the cellulose102330 processed with concentrated sulfuric acid is used.

The detailed conditions are as follows:

-   -   First concentration of metal ion: 0.1 mmol/L    -   Volume of the metal solution: 10 mL    -   Dry weight of the adsorbent A: 10 mg    -   Shaking time: 48 hours    -   Temperature: 30° C.

As shown in FIG. 2, although gold is adsorbed not less than 70% insubstantially entire range of the hydrochloric acid concentration,adsorption of all other metals can be disregarded. Precious metals otherthan gold and the base metal ions are not adsorbed at all. Therefore, itis appreciated that only gold can be selectively separated and collectedfrom other metal ions by using the adsorbent A.

FIG. 3 is a graph illustrating a relationship between the adsorptionpercentage (vertical axis) of some metal ions and the hydrochloric acidconcentration (horizontal axis), when an adsorbent B is used. Theadsorbent B is prepared by processing nonwoven fabric of pure absorbentcotton (e.g., COTTON CIEGAL of CHIYODA CO., LTD.) with concentratedsulfuric acid.

In the preparation of the adsorbent B, the pure cotton is processed withconcentrated sulfuric acid in a similar processing condition to that ofthe adsorbent A. Also, the adsorption percentage of the case of theadsorbent B is calculated in the similar manner to that of the case ofthe adsorbent A.

The detailed test conditions are as follows:

-   -   First concentration of metal ion: 0.2 mmol/L    -   Volume of the metal solution: 10 mL    -   Dry weight of the adsorbent B: 10 mg    -   Shaking time: 24 hours    -   Temperature: 30° C.

As shown in FIG. 3, although a small mount of palladium(II) and a smallamount of platinum(IV) are adsorbed, the base metals, such as iron andcopper, are not adsorbed. On the other hand, gold(III) is adsorbedalmost quantitatively in a range where the concentration of thehydrochloric acid is equal to or less than 2M.

FIG. 4 illustrates a relationship between the extraction percentage(vertical axis) of metals and the concentration of hydrochloric acid ina solvent extraction using undiluted dibutyl carbitol as a comparativeexample.

The detailed test conditions are as follows:

-   -   First concentration of metal ion: 0.2 mM    -   Shaking velocity: 138 rpm    -   Shaking time: 98 hours    -   Temperature: 30° C.    -   Organic-phase volume: 10 mL    -   Aqueous-phase volume: 10 mL

As shown in FIG. 4, in a range where the concentration of hydrochloricacid is equal to or greater than 2M, extraction of iron(III) increasesand thus the selectivity of gold noticeably reduces.

FIG. 5 is a graph illustrating a relationship between the adsorptionpercentage (vertical axis) of metal ions and the concentration ofhydrochloric acid (horizontal axis) of various kinds of metal ion in acase where commercially available weakly basic ion exchange resin (e.g.,DIAION WA30) containing a functional group of dimethylamine is used, asa comparative example.

The detailed test conditions are as follows:

-   -   First concentration of metal ion: 15 mg/L    -   Volume of the metal solution: 15 mL    -   Dry weight of an adsorbent: 20 mg    -   Shaking time: 24 hours    -   Temperature: 30° C.

As shown in FIG. 5, different from the cases using the above-describedcellulose-base adsorbents A, B, platinum(IV) and palladium(II) areadsorbed with the similar amount, in addition to gold(III). Further,zinc as the base metal is adsorbed approximately 30%, and iron isadsorbed approximately 40% in a high concentration region of thehydrochloric acid.

Accordingly, it is appreciated that the cellulose-base adsorbents A, Bof the embodiment have favorable selectivity of gold, as compared withthe commercially available adsorbent.

<Adsorption Isotherm>

FIG. 6 is a graph illustrating an adsorption isothermal line ofgold(III) at 30° C. of a case where the adsorbent A of the celluloseprocessed with the concentrated hydrochloric acid is used. That is, FIG.6 is a graph illustrating a relationship between the amount ofadsorption of gold (vertical axis) and a concentration of gold(horizontal axis) after the adsorption.

The detailed test conditions are as follows:

-   -   Hydrochloric acid concentration: 0.1 mol/L    -   Volume of hydrochloric acid: 10 mL    -   Weight (dry weight) of the adsorbent A: 10 mg    -   Shaking time: 150 hours    -   Temperature: 30° C.

As shown in FIG. 6, the adsorption isothermal line indicatesLangmuir-type adsorption. The saturation amount of gold adsorbed to theadsorbent A is calculated 8 mol/kg based on the value of the amount ofadsorption in a range where the amount of adsorption is fixed regardlessof the concentration. This results indicates that 1.6 kg of gold isadsorbed to 1 kg of the adsorbent A.

FIG. 7 is a graph illustrating an adsorption isothermal line ofgold(III) at 30° C. of a case where the adsorbent B of the cottonprocessed with concentrated hydrochloric acid is used.

The detailed test conditions are as follows:

-   -   Hydrochloric acid concentration: 0.1 mol/L    -   Volume of hydrochloric acid: 10 mL    -   Weight (dry weight) of the adsorbent B: 10 mg    -   Shaking time: 96 hours    -   Temperature: 30° C.

Also in this case, the adsorption isothermal line indicates theLangmuir-type adsorption. The saturation amount of gold adsorbed to theadsorbent B is calculated 6 mol/kg based on the value of the amount ofadsorption in a range where the amount of adsorption is fixed regardlessof the concentration. This result indicates that 1.2 kg of gold isadsorbed to 1 kg of the adsorbent B.

The adsorbent A is added to 0.25M hydrochloric acid containing gold(III)of thin concentration of 0.83 mg/L, and shaken for 24 hours at 30° C. tomeasure residual concentration of gold. Further, the measurement iscarried out by varying the amount of the adsorbent A. FIG. 8 is a graphillustrating a relationship between a solid-liquid ratio (a ratio of theadsorbent A and hydrochloric acid) and the residual concentration ofgold.

As a result, it is appreciated that the gold of thin concentration canalso be quantitatively collected by adding 1 g of the adsorbent A to 1 Lof a solution (hydrochloric acid).

The adsorbent B is added to 0.1M hydrochloric acid containing 0.2 mMgold(III), and shaken for 24 hours. The residual concentration of goldis measured. The measurement is carried out by varying the amount of theadsorbent B.

Further, a similar measurement is carried out using raw cotton, which isnot processed with concentrated sulfuric acid, in place of the adsorbentB of the cotton processed with the concentrated sulfuric acid.

FIG. 9 illustrates a relationship between the solid-liquid ratio (aratio of adsorbent and hydrochloric acid). In FIG. 9, the result of theadsorbent B is illustrated by a line of “cross-linked cotton”, and theresult of the raw cotton is illustrated by a line of “raw cotton”.

As shown in FIG. 9, it is appreciated that the gold can bequantitatively collected by adding approximately 1 g of the adsorbent Bto the solution of 1 L, although gold is not adsorbed to the raw cotton.

<Generation of Particles of Solid Gold>

Gold is adsorbed to the adsorbent A in the above-described manner, andthen the adsorbent A is extracted and dried. FIG. 10A illustrates anoptical micrograph of the dried adsorbent A.

Further, gold is adsorbed to the adsorbent B in the above-describedmanner, and then the adsorbent B is extracted and dried. FIG. 11Aillustrates an optical micrograph of the dried adsorbent B.

As shown in FIGS. 10A and 11A, it is considered that the gold(III) ironsadsorbed to the respective adsorbents A, B are returned to elementalgold and grown into gold particles. Further, it is considered that thelarge amount of adsorption of gold in the adsorbents A, B as shown inFIGS. 6 and 7 is caused by such growth of gold particles.

In this case, the gold is collected in the form of gold particles,rather than the state of gold(III) ions. Therefore, the gold is easilycollected.

The present disclosure is not limited to the above-described exemplaryembodiments, but may be implemented in various other ways withoutdeparting from the spirit of the present disclosure.

For example, the adsorbent may be prepared using carbohydrates otherthan cotton. As an example, the adsorbent can be prepared using paper.

The adsorbents A, B may be prepared by carrying out the dehydrationcondensation cross-linkage reaction using strong acid other thansulfuric acid, such as hydrochloric acid.

Additional advantages and modifications will readily occur to thoseskilled in the art. The disclosure in its broader term is therefore notlimited to the specific details, representative apparatus, andillustrative examples shown and described.

1. An adsorbent containing a carbohydrate having an ether linkage.
 2. Anadsorbent containing a carbohydrate having a cross-linkage formationprovided by a dehydration reaction using a strong acid.
 3. The adsorbentaccording to claim 2, wherein the strong acid includes one of sulfuricacid and hydrochloric acid.
 4. The adsorbent according to claim 2,wherein the carbohydrate includes a cellulose.
 5. The adsorbentaccording to claim 4, wherein the cellulose is one or more selected fromthe group consisting of cotton, hemp and paper.
 6. The adsorbentaccording to claim 1, wherein the carbohydrate includes a cellulose. 7.The adsorbent according to claim 6, wherein the cellulose is one or moreselected from the group consisting of cotton, hemp and paper.
 8. Amethod of collecting a precious metal dissolved in a solution,comprising: adsorbing the precious metal to the adsorbent according toclaim
 1. 9. A method of collecting a precious metal dissolved in asolution, comprising: adsorbing the precious metal to the adsorbentaccording to claim 2.